1. Field of the Invention
This invention relates in general to database management systems performed by computers, and in particular, to the efficient handling of exceptions during access plan execution in an On-Line Analytic Processing (OLAP) system.
2. Description of Related Art
On-Line Analytical Processing (OLAP) systems provide tools for analysis of multidimensional data. Most systems are built using a three-tier architecture, wherein the first or client tier provides a graphical user interface (GUI) or other application, the second or middle tier provides a multi-dimensional view of the data, and the third or server tier comprises a relational database management system (RDBMS) that stores the data.
Most queries in OLAP systems are complex and require access to large amounts of data. However, decision support applications in OLAP systems need to be interactive and demand fast response times. Different techniques to speed up queries have been studied and implemented, both in research and industrial systems.
Performance improvements have been assisted by enhancements to query processing schemes, such as parallel processing schemes that divide a query into smaller sub-units, each of which can be assigned to different processors, threads, or processes. These parallel processing schemes greatly increase the performance of OLAP systems, and ensure that queries are executed as quickly as possible.
Although the benefits of employing parallelism are widely known, it has also been noticed that increasing the degree of parallelism also increases the problems with exception handling. For example, when a large number of operators for a query are executed simultaneously, it may be very difficult to coordinate the operators when handling exceptions generated from only one or a few of the operators. This specification examines the question of how to handle exceptions for different, concurrently running operators of a query in a way that will coordinate the total query response.
A method, system and article of manufacture for performing queries in an in an On-Line Analytic Processing (OLAP) system. The method, system and article of manufacture provide improved handling of exceptions for different, concurrently running operators of a query in a way that will coordinate the total query response. The method comprises the steps of: (a) translating a query into an operator tree comprised of a plurality of operators; (b) independently executing each of the operators in the operator tree; (c) detecting an exception in one or more of the independently executed operators of the operator tree; and (d) propagating the detected exceptions to remaining ones of the independently executed operators of the operator tree by recycling empty data pages, piggybacking the detected exceptions on the recycled data pages, and sending the recycled data pages to the remaining ones of the independently executed operators of the operator tree in a bi-directional flow, wherein the detected exceptions are propagated downward as well as upward the operator tree. The system and article of manufacture embody logic for performing the method steps described above.